Light indicating system and method



Sept' l, 1931- G. R. FlsHER 1,821,698

LIGHT INDICATING SYSTEM AND METHOD Filed July l5, 1927 IN V EN TOR 6er/fara E. Fis/1er A TTORNE YS Panarea sept. 1, -1931 y UNH-lazo STATES PATENT' or-l-lcls GERHARD R. FISHER, F PALO' ALTO, CALIFORNIA, ASSGNOR TO FEDERAL TLEGRAPH COMPANY, 0F SAN FRANCISCO, CALIFORNIA, A CORPORATION 0F CALIFORNIA I `LIGHT INDICATIG SYSTEM AND METHOD Application illed July 13,

This' invention relates generally .to methods of and systems for securing an electrical indication in responsev to a change in light intensity. l A broad object of the invention is to provide an indicating device responsive to changes in light intensity.

Al feature of the invention is a sensitive light indicating device utilizing a rugged, cold electrode, gas discharge tube, 'whlch 1s 'ordinarily relatively insensitive to light variations.

AAnother feature is the combination of an oscillatory circuit comprising a light sensitive element with indicating 'means responsive only tov oscillatory current, the arran ef ment being such that variations in\light m"-l tensity cause the starting and stopping of oscillations in the' oscillatory circuit.

Referring to the drawings:

tube is intermittent or oscillatory rather than continuous. This characteristic is especially noticeable with gas'discharge tubes containing iieon gas. In operating tubes of this kind it has been noted that the frequency of the interruptions is affected by the intensity of light falling upon the tube, especially llght containing ultra-violet rays. For example when the light intensity is decreased, it has been noted that the frequency decreases and, conversely, when the light intensity increases the frequency tends to increase. While it is possible to utilize this change in frequency to secure an (indicationof a variation in light intensi-ty, apparatus which is designed to indicate light lnte'nsity by frequency changes is unreliable in operation and diiicult to calibrate.

In experiments which I have vconducted in order to determine the effect of varying 1927. Serial N0. 205,343.

light intensities upon an oscillating neon tube, I discovered that the tube can be adjusted to a critical condition for a given light intensity at which the oscillatory current is zero. However with the tube in this critical condition, only a slight decrease in light intensity is suiiicient to cause the tube to start oscillating, thus causing a sudden increase in the oscillatory current from zero includes a source of direct potential such as the battery 11 and a relatively high series resistance 12. The gas discharge tube is .preferably of the neon ty'pe and comprises for example an evacuated vessel vcontaining a smallamount of neon gas at a pressure of from 6 to 8 millimeters of mercury. The anode 13 and cathode 14 of this tube are preferably made of suitable metal and during normal operation remain relatively cold., Shunted across the tube electrodes, is avari` able condenser 16 which aids in controlling operation ofthe tube.

With the circuit as described, if the Ypotential of battery 11 is sufficiently high and if resistance 12 is of the correct value, an interrupted How of current will occur across the electrodes', the frequency of which `may be determined principally by the capacitance of condenser 16. As the value of resistance 12 is decreased, a condition will be reached at which the oscillatory current will `fall to substantially zero, although a direct current will continue to How. Now if the light intensity falling uponthe tube is decreased, the tube again starts to oscillate and there is a sudden rise in oscillatory current'fiow in the exciting circuit from substantially` `zero `to a relatively high value. Generally thehigher the frequency of oscillation produced by a given decrease in light intensity, the more sensitivethe device will be to light changes.

The sudden increase in oscillatory current in the exciting circuit may be translated by any suitable apparatus to secure an indication of the decrease ih light intensity. For example I have shown a relay 17 of the electron relay type having its input circuit inductively coupled to the exciting circuit of tube 10. In this particular instance a coupling transformer 18 is provided, having its primary winding included 1n the exciting circuit in series with battery 11,v and its secondary connected to the input circuit of relay 17. A suitable translator such as a telephone 19, is included in the output circuit of relay 17. If it is desired vto indicate a decrease in light intensity, the characteristics of the exciting circuit are adgg justed as by varying the value of resistance 12, and the value of condenser 16, so that for a given light intensity the tube is near the point of oscillation. When the .light in tensity decreases the tube is set into osclllag5 tion and the oscillations are heard in the receiver. ,y

In Fig. 2 I have indicated how this method may be incorporated with a Sextant for taking observations. based on the angular position of thesun. In this case the gas discharge tube 10. is placed adjacent the pivot point of the index arm 21. This index arm cooperates with the graduated scale 22 and carries a screen 23 which is adapted 36 to cast a shadow upon tube 10 when moved to a position which will indicate the angular position of the sun. To provide for visual indicating means I have shown the exciting circuit coupled to a plurality of amplifiers 26 and 27 which energize a suitable indicating lamp, such as the neon lamp 28. In operating this apparatus the resistance 12 is decreased just past the point Where for a given light intensity substantially no current flow occurs in the exciting circuit and the lamp 28 is extinguished. The index arm 21 is then'moved until a shadow falls upon tube 10, and because of the decrease inlight intensity, a rush of interrupted cur- -rent will flow in the exciting circuit and lamp 28 will be illuminated-bv the amplified energy. y

I'claii'n:

1. A method of operating a gas discharge tube having cold electrodes in order to detect variations in light intensity, the method being characterized by the use of an energizing circuit for the tube including a source of direct current, and a relatively high resistance in series With said source, said method comprising adjusting the values of the circuit so that-substantially,y no oscillatory current flow occurs for a given light t5y intensity falling on the tube, but so that' 'means for energizing said tube, said tube oscillatory current ilow occurs for a. slightly decreased light intensity. I l

`2. Ina. system of the 'class described, a. gas discharge tube having cold electrodes, being adjusted to a. critical condition at 7o which a substantial decrease in light intensity falling on the tube will initiate an interrupted current flow through the same, and means for varying the light intensity falling upon the tube.

3. In a device for indicating in light intensity, the combination of a source of electrical oscillations containing as a controlling element thereof a light sensitive element for starting and stopping oscillations, and indicating means responsive only to oscillatory current from said source.

4. Means as described in claim 2 further characterized in that said gas discharge device contains neon.

5, A system for detecting variations in intensity of light, comprising a light sensitive discharge tube exposed to the light a variation of which is to be detected, means for energizing said tube whereby it produces an oscillatory current, and indicating means responsive to a changeV in said oscillatory current to indicate f a change in intensity of said light.

6. A system for detecting variations in intensity of light comprising a light sensitive discharge device, the impedance of which varies inversely with the current therethrough, a source of current and an ini-J 100 pedance element connected in series with said discharge device and a capacitance connected in shunt thereto, whereby oscillations are produced, a variable source of light to which said discharge device is exposed, and indicating means responsive to a change in said oscillations to indicate a change in said light intensity.

In testimony whereof, I have hereunto set my hand.

' GERHARD R. FISHER. 

